Geological Survey of Tanzania

Dodoma, Tanzania

Geological Survey of Tanzania

Dodoma, Tanzania
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Macheyeki A.S.,Geological Survey of Tanzania | Mdala H.,Geological Survey of Malawi | Chapola L.S.,The Catholic University of Malawi | Manhica V.J.,National Directorate of Geology | And 14 more authors.
Journal of African Earth Sciences | Year: 2015

The East African Rift System (EARS) has natural hazards - earthquakes, volcanic eruptions, and landslides along the faulted margins, and in response to ground shaking. Strong damaging earthquakes have been occurring in the region along the EARS throughout historical time, example being the 7.4 (Ms) of December 1910. The most recent damaging earthquake is the Karonga earthquake in Malawi, which occurred on 19th December, 2009 with a magnitude of 6.2 (Ms). The earthquake claimed four lives and destroyed over 5000 houses. In its effort to improve seismic hazard assessment in the region, Eastern and Southern Africa Seismological Working Group (ESARSWG) under the sponsorship of the International Program on Physical Sciences (IPPS) carried out a study on active fault mapping in the region. The fieldwork employed geological and geophysical techniques. The geophysical techniques employed are ground magnetic, seismic refraction and resistivity surveys but are reported elsewhere. This article gives findings from geological techniques. The geological techniques aimed primarily at mapping of active faults in the area in order to delineate presence or absence of fault segments. Results show that the Karonga fault (the Karonga fault here referred to as the fault that ruptured to the surface following the 6th-19th December 2009 earthquake events in the Karonga area) is about 9. km long and dominated by dip slip faulting with dextral and insignificant sinistral components and it is made up of 3-4 segments of length 2-3. km. The segments are characterized by both left and right steps.Although field mapping show only 9. km of surface rupture, maximum vertical offset of about 43. cm imply that the surface rupture was in little excess of 14. km that corresponds with Mw = 6.4. We recommend the use or integration of multidisciplinary techniques in order to better understand the fault history, mechanism and other behavior of the fault/s for better urban planning in the area. © 2014 Elsevier Ltd.

Kabete J.M.,AngloGold Ashanti | McNaughton N.J.,Curtin University Australia | Groves D.I.,Canaco Resources Inc. | Mruma A.H.,Geological Survey of Tanzania
Precambrian Research | Year: 2012

Reconnaissance U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon dating of gneisses, granitoids and greenstones from well-documented study areas within the Tanzania Craton indicates that: (1) ~2815-2691 Ma greenschist-amphibolite facies greenstones and associated granitoids are confined within extensive >3600 Ma granitoid-gneisses in the Central Tanzania Region; (2) greenschist-amphibolite facies greenstone rocks from the Singida-Mayamaya Terrane in the south-eastern Lake Nyanza Superterrane, Lake Victoria Region are older than 2681 Ma; (3) greenschist to lower-granulite facies granitoid-greenstone belts from the Kilindi-Handeni Superterrane, within the largely Neoproterozoic Southern East African Orogen are older than 2670 Ma; and (4) the granitoid-greenstone belts within the Dodoma Basement Superterrane, Central Tanzania Region and Kilindi-Handeni Superterrane, Southern East African Orogen are broadly coeval with ~2823-2671 Ma granitoid-greenstone belts in the Lake Nyanza Superterrane, in the Lake Victoria Region.The basement to juvenile greenstone rocks in the Central Tanzania Region includes E-W-trending orthogneisses. These comprise largely >3140 Ma diorite to granodiorite gneisses with rafts and/or tectonic enclaves of supracrustal rocks, including ~3600 Ma fuchsitic sericite quartzite, which forms part of the ~25. km by 5. km Simba-Nguru Hills in the Undewa-Ilangali Terrane. This quartzite contains detrital 4013-3600 Ma zircons that define ancestral cycles of protracted magmatism in their as yet undetected source terranes.In addition to the ~2815-2670 Ma granitoids and greenstones in the >3000 Ma gneisses and granitoids within the widely accepted marginal zone of the Tanzania Craton, the Lake Nyanza Superterrane extends east into the Kilindi-Handeni Superterrane, in the largely Neoproterozoic Southern East African Orogen. In this Superterrane, Neoarchean igneous and sedimentary rocks in the Mkurumu-Magamba Terrane record ~620-603 Ma amphibolite-granulite facies metamorphism, ~585-575 Ma partial-melting, and emplacement of enderbitic-charnockitic granitoids. They also record a short-lived, but significant, 570-560 Ma period of exhumation and emplacement of high-grade metamorphic rocks on to basement rocks of the proto-Archean craton within the Central Tectonic Zone in the Southern East African Orogen. © 2012 Elsevier B.V.

Kabete J.M.,AngloGold Ashanti | Groves D.I.,Canaco Resources Inc | McNaughton N.J.,Curtin University Australia | Mruma A.H.,Geological Survey of Tanzania
Ore Geology Reviews | Year: 2012

The lack of new gold discoveries in recent times has prompted suggestions that Tanzania is mature or approaching maturity, in terms of gold exploration. New tectonic-metallogenic subdivisions proposed in this study are used to explain gold-endowment, assess gold exploration maturity, and suggest the potential for new discoveries from the following three regions: 1) the Lake Victoria Region, comprising the gold-endowed East Lake Victoria and Lake Nyanza Superterranes of <2.85. Ga greenschist-amphibolite facies granitoid-greenstone terranes in >3.11. Ga continental crust. These superterranes are separated by the gold-poor, Mwanza-Lake Eyasi Superterrane, comprising deeply eroded and/or exhumed terranes of gneissic-granulite belts and widespread granitoid plutons; 2) the Central Tanzania Region, comprising the Moyowosi-Manyoni Superterrane, which is largely composed of granitoid and migmatitic-gneissic terranes, and the Dodoma Basement and Dodoma Schist Superterranes, these are underlain by extensive, >3.2. Ga migmatitic-gneisses and granitoid belts with interspersed, relatively narrow, <2.85. Ga greenschist-amphibolite facies greenstone and schist belts. The Central Tanzania Region also includes the East Ubendian-Mtera Superterrane, comprising the East Ubendian Terrane of predominantly Paleoproterozoic belts with cryptic Archean age components, and the ~2.85-3.0. Ga Isanga-Mtera Terrane of thrust-transported migmatitic ortho- and para-gneisses; and 3) Proterozoic Tanzania Regions, comprising various Archean terranes which were once sutured to the Tanzania Craton prior to later Proterozoic orogenic and tectonic events that separated them from the craton and thermally reworked them. These include the Archean Nyakahura-Burigi Terrane in the Northwestern Tanzania Proterozoic Orogen and the Kilindi-Handeni Superterrane in the Southern East African Orogen of Tanzania. The major metallogenic significance of the new tectonic subdivisions is the recognition of under-explored belts: 1) in the gold-endowed East Lake Victoria and Lake Nyanza Superterranes, Lake Victoria Region. Here deeply weathered belts in the Musoma-Kilimafedha, Kahama-Mwadui and Nzega-Sekenke Terranes and belts, situated in tectono-thermally reworked crustal blocks such as the Iaida-Haidon, Singida-Mayamaya and Mara-Mobrama Terranes, are predicted to be prospective; 2) in the Dodoma Basement Superterrane, Central Tanzania Region, where relatively thin, juvenile granitoid-greenstone belts, similar to the ~2815-2660. Ma Mazoka Belt in the Undewa-Ilangali Terrane, contain small-scale gold systems with analogous terrane-scale geologic settings and evolution histories to those of gold-hosting greenstone belts in the Sukumaland Terrane, Lake Victoria Region. The overall geologic-geometric setting of the greenstone belts in the Central Tanzania Region (Mazoka-type) is comparable to those of the gold-hosting juvenile granitoid-greenstone belts in the South West and Youanmi Terranes, Yilgarn Craton, Western Australia, and North Superior and North Caribou Superterrane, northwestern Superior Craton, Canada; and 3) in the Proterozoic Tanzanian Regions, where terranes that lie in close geographic proximity and regional strike extension to the gold-endowed Lake Nyanza Superterrane are likely to be most prospective. They include the Archean Nyakahura-Burigi Terrane in unroofed thrust windows of the Mesoproterozoic Karagwe-Ankolean Belt of northwestern Tanzania, and the Kilindi-Handeni Superterrane where Archean proto-crust has been reworked by Pan-African tectonothermal events in the Southern East African Orogen. © 2012 Elsevier B.V.

Thomas R.J.,British Geological Survey | Bushi A.M.,Geological Survey of Tanzania | Roberts N.M.W.,British Geological Survey | Jacobs J.,University of Bergen | Jacobs J.,Norwegian Polar Institute
Journal of African Earth Sciences | Year: 2014

New U-Pb zircon LA-ICP-MS data are presented for 4 granitoid bodies which intrude high grade gneisses of the previously unmapped Ruangwa region in southern Tanzania. The study area forms part of the late Neoproterozoic East African Orogen (EAO). The oldest unit, a coarse-grained migmatitic granitic orthogneiss gave an early Neoproterozoic (Tonian) crystallization age of 899. ±. 9/16. Ma, which is similar to, but significantly younger than, Stenian-Tonian basement ages in areas relatively nearby. Crust of this age may extend as far north as the major Phanerozoic Selous Basin, north of which Archaean protolith ages predominate (the "Western Granulites"), except for the juvenile Neoproterozoic "Eastern Granulites", which are not represented in the study area. To the south, the Tonian crust of the study area provides a tentative link with the Marrupa Complex in NE Mozambique. A granite pluton, dated at 650. ±. 5/11. Ma is broadly coeval with the main Pan-African tectono-thermal event in the East African Orogen that is recorded across Tanzania north of the Selous Basin. Zircons in this granite contain inherited cores at ca. 770. Ma. This age is within the range of dates obtained from south and west of the study area from juvenile granitoid orthogneisses which might be related to a widespread, but poorly understood, early phase of Gondwana assembly along an Andean-type margin.South of the study area, in NE Mozambique, the latest orogenic events occurred at ca. 550. Ma, and are sometimes attributed to the Ediacaran-aged "Kuunga Orogeny". While metamorphic dates of this age have been recorded from the EAO north of the Selous Basin, magmatic rocks of this event have not been recognized in Tanzania. The two youngest granitoids of the present study are thus the first 500-600. Ma igneous rocks reported from the region. A weakly deformed very coarse-grained granite pluton was dated at 591. ±. 4/10. Ma, while a very late, cross-cutting, undeformed granite dyke gave an intrusive age of 549. ±. 4/9. Ma.The granitoids ages presented in this study contain elements that are characteristic of the northern, Tanzania-Kenya, segment of the East African Orogen and of the southern, Mozambique, segment. The Tonian orthogneiss sample is typical of (but somewhat younger than) the Marrupa Complex of NE Mozambique. No zircon inheritance was recorded in the sample, typical of the juvenile Marrupa Complex. On the other hand, the ca. 650. Ma granite pluton has an age that is typical of the northern segment of the orogen; this is the first recorded granite of that age intruded into the Tonian-dominated crust of southern Tanzania or NE Mozambique. The two younger granites have provided dates that are typical of the southern segment of the orogen, and that of the Kuunga Orogen. The study area thus appears to represent an area of transitional crust straddling two complex and contrasting segments of the East African Orogen, with elements of both segments present and evidence for a ca. 770. Ma event which appears to be quite widespread and may relate to the early phases of Gondwana amalgamation in southern East Africa. © 2014 The Authors.

Thomas R.J.,Council for Geoscience | Spencer C.,British Geological Survey | Spencer C.,Curtin University Australia | Bushi A.M.,Geological Survey of Tanzania | And 21 more authors.
Precambrian Research | Year: 2016

Geological mapping and zircon U-Pb/Hf isotope data from 35 samples from the central Tanzania Craton and surrounding orogenic belts to the south and east allow a revised model of Precambrian crustal evolution of this part of East Africa. The geochronology of two studied segments of the craton shows them to be essentially the same, suggesting that they form a contiguous crustal section dominated by granitoid plutons. The oldest orthogneisses are dated at ca. 2820 Ma (Dodoma Suite) and the youngest alkaline syenite plutons at ca. 2610 Ma (Singida Suite). Plutonism was interrupted by a period of deposition of volcano-sedimentary rocks metamorphosed to greenschist facies, directly dated by a pyroclastic metavolcanic rock which gave an age of ca. 2725 Ma. This is supported by detrital zircons from psammitic metasedimentary rocks, which indicate a maximum depositional age of ca. 2740 Ma, with additional detrital sources 2820 and 2940 Ma. Thus, 200 Ma of episodic magmatism in this part of the Tanzania Craton was punctuated by a period of uplift, exhumation, erosion and clastic sedimentation/volcanism, followed by burial and renewed granitic to syenitic magmatism. In eastern Tanzania (Handeni block), in the heart of the East African Orogen, all the dated orthogneisses and charnockites (apart from those of the overthrust Neoproterozoic granulite nappes), have Neoarchaean protolith ages within a narrow range between 2710 and 2630 Ma, identical to (but more restricted than) the ages of the Singida Suite. They show evidence of Ediacaran "Pan-African" isotopic disturbance, but this is poorly defined. In contrast, granulite samples from the Wami Complex nappe were dated at ca. 605 and ca. 675 Ma, coeval with previous dates of the "Eastern Granulites" of eastern Tanzania and granulite nappes of adjacent NE Mozambique. To the south of the Tanzania Craton, samples of orthogneiss from the northern part of the Lupa area were dated at ca. 2730 Ma and clearly belong to the Tanzania Craton. However, granitoid samples from the southern part of the Lupa "block" have Palaeoproterozoic (Ubendian) intrusive ages of ca. 1920 Ma. Outcrops further south, at the northern tip of Lake Malawi, mark the SE continuation of the Ubendian belt, albeit with slightly younger ages of igneous rocks (ca. 1870-1900 Ma) which provide a link with the Ponte Messuli Complex, along strike to the SE in northern Mozambique. In SW Tanzania, rocks from the Mgazini area gave Ubendian protolith ages of ca. 1980-1800 Ma, but these rocks underwent Late Mesoproterozoic high-grade metamorphism between 1015 and 1040 Ma. One granitoid gave a crystallisation age of ca. 1080 Ma correlating with known Mesoproterozoic crust to the east in SE Tanzania and NE Mozambique. However, while the crust in the Mgazini area was clearly one of original Ubendian age, reworked and intruded by granitoids at ca. 1 Ga, the crust of SE Tanzania is a mixed Mesoproterozoic terrane and a continuation from NE Mozambique. Hence the Mgazini area lies at the edge of the Ubendian belt which was re-worked during the Mesoproterozoic orogen (South Irumide belt), providing a further constraint on the distribution of ca. 1 Ga crust in SE Africa.Hf data from near-concordant analyses of detrital zircons from a sample from the Tanzania Craton lie along a Pb-loss trajectory (Lu/Hf = 0), extending back to ~3.9 Ga. This probably represents the initial depleted mantle extraction event of the cratonic core. Furthermore, the Hf data from all igneous samples, regardless of age, from the entire study area (including the Neoproterozoic granulite nappes) show a shallow evolution trend (Lu/Hf = 0.028) extending back to the same mantle extraction age. This implies the entire Tanzanian crust sampled in this study represents over 3.5 billion years of crustal reworking from a single crustal reservoir and that the innermost core of the Tanzanian Craton that was subsequently reworked was composed of a very depleted, mafic source with a very high Lu/Hf ratio. Our study helps to define the architecture of the Tanzanian Craton and its evolution from a single age-source in the early Eoarchaean. © 2016 Elsevier B.V.

Thomas R.J.,British Geological Survey | Roberts N.M.W.,British Geological Survey | Jacobs J.,University of Bergen | Bushi A.M.,Geological Survey of Tanzania | And 2 more authors.
Precambrian Research | Year: 2013

A study of the position, nature and geochronology of the eastern margin of the Tanzania Craton near Mpwapwa yields new constraints on Archaean to Neoproterozoic orogenesis of central Tanzania. The eastern part of the craton comprises typical Neoarchaean grey granodioritic orthogneisses dated with the LA-ICP-MS method by U-Pb zircon at ca. 2.7. Ga. A gradual eastward increase in strain in these rocks culminates in a 1-2. km wide, locally imbricated, north-south-trending, ductile thrust/shear zone with an oblique top-to-the-NW sense of movement. East of the craton-edge shear zone, high-grade supracrustal rocks are termed the " Mpwapwa Group" in view of uncertain regional correlations. There is an apparent lithological zonation of the Mpwapwa Group parallel to the craton margin shear zone. In the west, the group consists of typical " shelf facies" metasedimentary rocks (marbles, calc-silicates, quartzites, etc.). U-Pb dating of detrital zircons from two quartzites reveal only Archaean detritus, constraining their maximum depositional age to ca. 2300. Ma) with a strong metamorphic overprint at ca. 1960. Ma (zircon), confirmed by a metamorphic titanite age of ca. 1990. Ma, again believed to date the initial phase of craton-margin shearing and juxtaposition of the Archaean crustal blocks. The role of the Neoproterozoic East African orogeny in the evolution of the craton margin is unclear, but the geometry of the shear zone, the presence of Neoproterozoic zircon rims in the Palaeoproterozoic granite and published studies from nearby, all suggest that the latest movements on the shear zone may be Neoproterozoic in age and that the structure may represent the local western front of the East African Orogeny. © 2012 Elsevier B.V.

Delvaux D.,Royal Museum for Central Africa | Kervyn F.,Royal Museum for Central Africa | Macheyeki A.S.,The University of Dodoma | Macheyeki A.S.,Mineral Resources Institute | Temu E.B.,Geological Survey of Tanzania
Journal of Structural Geology | Year: 2012

The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in an NW-SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E-W extension for the entire EARS. The central part of the TRM rift segment is well exposed in the Ufipa plateau and Rukwa basin, within the Paleoproterozoic Ubende belt. It is also one of the most seismically active regions of the EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage is the best expressed in the field and caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting (our third and last stress stage). © 2012 Elsevier Ltd.

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